FRESNO – Federal officials said Friday they had cut back the amount of water pumped to farmers and Southern California cities to the lowest level ever in an attempt to help save the endangered delta smelt.

The decision comes a day after state officials temporarily halted operations at their main pumping plant and has raised concern among farmers that their crops may not get sufficient water.

The U.S. Bureau of Reclamation will continue to operate just one pump that draws from the Sacramento-San Joaquin Delta for at least another week, in light of a recent survey that found the smelt population at an all-time low.

Federal authorities also plan to buy extra water supplies to accommodate cities and farms and to diminish the sucking power of the powerful pumps, which have been blamed for killing the smelt and other fish when they send water from the delta into the California Aqueduct.

“We’ll do everything we can to protect this fish,” bureau spokesman Jeff McCracken said.

Friday’s announcement was just the latest development in the fight to save the smelt, a silvery, three-inch-long species protected under the California Endangered Species Act.

It is considered a bellwether for the health of the delta, a vast ecosystem that also provides drinking water to 25 million

Californians.

On Thursday, state officials shut down the massive pumps they operate near Tracy for seven to 10 days, a move supported by environmentalists who have long pushed for the species’ protection.

Most farms and cities won’t notice any difference in water supply, but three water districts in the San Francisco Bay area will have to draw extra water from local lakes, reservoirs and groundwater supplies to meet their needs, Department of Water Resources officials said.

The fate of the smelt also hinges on the outcome of two lawsuits.

In April, an Alameda County Superior Court judge ordered the state to stop pumping water from the delta within 60 days.